1. Field of the Invention
The present invention relates to a technique suitable for use in a thin-type inner-rotor motor for driving to rotate a media used in, for example, a floppy disk drive and so forth.
2. Description of the Related Art
The floppy disk drive and other disk drives are widely employed in the field from the personal computer to the office computer and the word processor, and so forth, which shows remarkable popularization. This type of disk drive is made up as shown in FIG. 10, for example.
This will be outlined on the basis of the drawing. In FIG. 10, the symbol 101 signifies a chassis, which possesses a spindle center 102 as the rotational center of a disk, which is housed in, for example, an equipment enclosure (not illustrated) of the personal computer. On the whole, the chassis opens to the front and to the upper, and is formed into a box with the bottom having a space to house a disk cartridge 103.
The chassis 101 has a stepping motor 124 for feeding a head carriage on the rear thereof, and the stepping motor 124 freely travels the head carriage forward backward. The head carriage holds a first head 130 on the front thereof, which reads information recorded on a disk. On the rear upper of the head carriage is attached a head arm 132 that freely swings through an elastic body, which has a second head 131 corresponding to the first head 130. The head arm 132 is energized in the direction that the second head 131 approaches to the first head 130. This type of disk drive is furnished with a cartridge holder 136 that holds the disk cartridge 103 to be freely pulled out, and a mechanism that opens and shuts the shutter of the disk cartridge 103.
Now, in order to satisfy the demand for a thinner type in recent years, this type of disk drive has been adopting one provided with an inner-rotor motor as illustrated in FIG. 11A and FIG. 11B as the motor for rotating a disk.
The inner-rotor motor is composed of a stator 164 and a rotor 166. The stator 164 has an annular yoke 161 extending circumferentially, and multiple cores 163 having coils 162 wound, which are provided radially on the inner periphery of the yoke 161. The rotor 166 has an annular magnet 165 installed to freely rotate on the inside of the stator 164, which faces to the cores 163. And, the symbol 168 denotes a circuit board on which is mounted a holder 170 incorporating bearings 169. The symbol 171 denotes a spindle for fixing the rotor that is pivoted to freely rotate through the bearings 169 on the holder 170 on the circuit board 168, which has the vertically extending axis. Further, the rotor 166 of this inner-rotor motor functions as a turntable having a disk chucking magnet (not illustrated) and a disk chucking swing lever (not illustrated).
In the stator for this type of inner-rotor motor, the yoke 161 and the cores 163 are placed to surround almost all the circumferences of the round rotor 166 except for the moving range of the heads 130 and 131. From the requirements of the magnetic characteristics of these, the yoke 161 and the cores 163 are formed of, for example, a silicon steel plate that is expensive in comparison to a galvanized sheet iron to form the chassis 101 and so forth.
However, in this type of disk drive, there has been an unremitting demand for reducing the production cost thereof, and still a strong demand for a smaller size and lighter weight of the drive.
Therefore, the inventor considers that there has been a demand for reducing the area of the yoke 161 and the cores 163 made of the expensive silicon steel plate, in the stator for the inner-rotor motor.
However, when the area of the yoke 161 and the cores 163 is reduced according to the foregoing demand, there has been found a possibility that the magnetic mutual effect to the rotor 166 becomes circumferentially nonuniform and the operational stability of the disk cannot be maintained accordingly.
Further, it is conceivable to divide the cores so as to have three yokes, in order to reduce the area of the cores 163. In this case, since the yokes each are placed in parallel, the spacings of the fronts each of the yokes become too narrow, and the coil winding cannot be performed, which is a problem.
The present invention has been made in view of the aforementioned circumstances, and the object of the invention is to achieve the following:
(a) reducing the production cost,
(b) making the drive smaller and lighter,
(c) maintaining the rotational stability of the motor,
(d) enhancing the operational stability of the disk drive,
(e) stepping up miniaturization of the stator.
According to one aspect of the invention, to accomplish the above object, the inner-rotor motor includes a rotor having plural magnetic poles disposed circumferentially, and a stator having a stator core with plural magnetic pole teeth facing to the rotor, located outside a circumference of the rotor, which have coils each wound around thereof.
In this construction, the coils are set such that the numbers of turns of adjacent coils are unequal, and respective sums of the numbers of turns of the coils in respective phases are equal.
In the invention, the windings of the coils may be set such that lengths of adjacent windings of the coils are unequal, and respective sums of the lengths of the windings corresponding to respective phases of the coils are equal.
In the invention, the coils may be placed such that at least one of points at which the extensions of lines connecting base end centers and front end centers of the adjacent coils intersect is positioned on an opposite side to the coils with regard to a rotational center of the rotor.
Further, in the invention, preferably the coils are arranged such that the base end centers of the adjacent coils are each placed with an equal spacing.
Further, in the invention, preferably the stator is placed within a central angel 180xc2x0 with regard to a rotational center of the rotor.
Further, in the invention, preferably the stator is provided with six of the coils.
The disk drive of the invention may be configured with the aforementioned inner-rotor motor.
According to this invention, the coils of the stator is configured by setting the numbers of turns of adjacent coils to be unequal, and respective sums of the numbers of turns of the coils in respective phases to be equal. Thereby, even when the lengths of the magnetic pole teeth are made unequally because the spacings of the adjacent coils are reduced for miniaturization, the uniformity of drive in respective phases of the coils can be achieved, the decrease of torque can be prevented, and the effective drive and rotational stability of the rotor can be accomplished.
According to this invention, the windings of the coils are made up by setting the lengths of adjacent windings to be unequal, and respective sums of the lengths of the windings corresponding to respective phases of the coils to be equal. Thereby, it is possible to avoid a situation where the coil winding becomes impossible even when the spacings of the adjacent magnetic pole teeth become extremely small, and to achieve miniaturization of the coil portion with a constant thickness of the coils in the coil windings.
Here, the base end center represents the center position of a part where the magnetic pole teeth with the coil formed thereon is connected to the yoke in the circumferential direction of the rotor, and the front end center represents the center position of the rotor facing side of the magnetic pole teeth of the front of the coil in the circumferential direction of the rotor.
The coils according to the invention can be placed such that at least one of the points at which the extensions of the lines connecting the base end centers and front end centers of the adjacent coils intersect is positioned on the opposite side to the coils with regard to the rotational center of the rotor. Thereby, in correspondence with the front end centers of the coils arranged with an equal spacing along the circumference of the rotor, further miniaturization of the stator can be achieved, and also the spacing of the magnetic pole teeth can be set so as to make the coil winding possible.
Further, in the invention, the coils can be placed in a state that the base end centers of the adjacent coils are each set with an equal spacing. Thereby, the magnetic pole teeth can be placed symmetrically with the points at which the extensions of the lines connecting the base end centers and front end centers of the adjacent coils intersect. Thereby, in correspondence with the front end centers of the magnetic pole teeth arranged with an equal spacing along the circumference of the rotor, still further miniaturization of the stator can be achieved, and also the spacing of the magnetic pole teeth can be set so as to make the coil winding possible.
Further, the base end centers of the coils can be set with an equal distance from the point positioned on the opposite side to the coils with regard to the rotational center of the rotor. Thereby, the shape of the yoke where the magnetic pole teeth are connected can be made into a simple circle to reduce the production cost.
Further, according to the invention, since the stator is located within the central angel 180xc2x0 with regard to the rotational center of the rotor, it becomes possible to reduce the area of the stator core less than about half, compared to the structure in which the stator is provided on the whole circumference of the rotor, such as a conventional inner-rotor motor. This construction reduces the cost of the stator core made of, for example, a silicon steel plate, and the cost of the coil winding and so forth, whereby the production cost of the inner-rotor motor can be cut down. Also, compared to the structure in which the stator is provided on the whole circumference of the rotor, it becomes possible to shrink the area for mounting the motor, to miniaturize the motor, and to lighten the motor by reducing the number of the magnetic pole teeth.
Further, the stator can take on a structure having a continuous central angel less than 180xc2x0 with regard to the rotational center of the rotor, or the stator can be made up with plural stator portions with intervals in-between, where the total sum of the central angles of the stator portions is within 180xc2x0. And, since the stator can be placed within the central angel 90xc2x0 with regard to the rotational center of the rotor, it becomes possible to achieve still further reduction of the production cost and the weight, and further miniaturization.
Further, since the stator is provided with six coils, the motor of the invention can be applied to the three-phase inner-rotor motor.